In most animals it evolved to help them stay warm, but elephants use their hair to cool off, according to a new study.

Scientists have found that the sparse bristles of hair covering the skin of the largest living animals to walk on land can dissipate heat.

Unlike most mammals, where dense body hair insulates against the cold, elephant hairs can increase heat loss by up to 20 per cent.

It is the latest adaptation found in elephants to help them cope with the sweltering heat of their African and Asian habitats.

Biologists have long known that elephants use their distinctive large ears and bathing in rivers to keep cool in such hot climates, but recent research revealed their bodies are also covered in “hot spots” that help them shed excess heat.

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The latest surprising discovery provides a new insight into how such large animals are able to survive in areas of the world like the African Savannah and India, where temperatures rarely dip below 25 degrees C.

Professor Elie Bou-Zeid, an environmental engineer from Princeton University who led the research, said: “Hair works as an insulator when it covers the skin. We show that sparse hair has the opposite effect.

“Sparse hair increases heat dissipation from the skin of elephants. What was surprising to us when was the magnitude we found for this effect.”

Elephants have the highest ratio of body mass to skin surface in any land animal, meaning they should struggle to control their body temperature in hot conditions. Smaller animals tend to cope better in hot conditions.

Using experiments with a range of different densities of hair, however, the scientists discovered that elephant hair was sparse enough to wicks heat away from the skin, allowing it to dissipate into the air more easily.

In still conditions sparse hair increased heat loss by five per cent and up to 23 per cent in a light breeze.

They said that hair switches from being an insulator to being a heat dissipater when there are fewer than 300,000 hairs per square metre (10 square feet).

Elephants have around 1,500 hairs per square metre while the human head has 2 million per square metre.

The researchers, whose study is published in the scientific journal PLOS One, speculate that body hair may have first evolved as a way of staying cool rather than staying warm.

Conor Myhrvold, the lead author on the study, said: “the heat transfer effect of elephant hair challenges the belief that a sparse hair layer would have provided insulation early on in its evolutionary development.

“It could therefore be a first step to resolving the prior paradox of why hair was able to evolve in a world much warmer than our own.”